| Document and Entity Information Document | Mar. 03, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | May 12, 2022 |
| Entity Registrant Name | Duolingo, Inc. |
| Entity Central Index Key | 0001562088 |
| Amendment Flag | false |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-40653 |
| Entity Tax Identification Number | 45-3055872 |
| Entity Address, Address Line One | 5900 Penn Avenue |
| Entity Address, City or Town | Pittsburgh |
| Entity Address, State or Province | PA |
| Entity Address, Postal Zip Code | 15206 |
| City Area Code | 412 |
| Local Phone Number | 567-6602 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Class A common stock, $0.0001 par value per share |
| Trading Symbol | DUOL |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Security Exchange Name | NASDAQ |
